1. Field of the Invention
The present invention relates to a lens barrier opening/closing device for opening and closing a lens barrier which is disposed in a front end of a movable lens barrel for the purpose of preventing the front surface of the lens from being stained or damaged.
2. Description of the Related Art
A zoom lens of a camera which has a movable barrel driven to advance from a housed position (accommodation position) to a photographing position when the power is turned ON is known in the art. Such a zoom lens which is provided in the front end thereof with a lens barrier (which generally has a plurality of movable barrier blades) that is driven to open and close a forefront photographic aperture of the zoom lens by moving the movable barrel of the zoom lens from the housed position to the advance position and from the advance position to the housed position, in that order, is also known in the art.
In one of the lens barriers of this type, a barrier drive ring is provided to be rotatable about the optical axis of the zoom lens to open and close the barrier blades. The barrier drive ring is constantly biased toward one rotational end thereof to open the barrier blades by a spring. A rearward movement of the movable barrel of the zoom lens from the photographing position to the housed position causes another movable member of the zoom lens to be engaged with the barrier drive ring to rotate the same in one direction to close the barrier blades against the spring force. Conversely, a forward movement of the movable barrel of the zoom lens from the housed position to the photographing position causes the above-mentioned movable member to be disengaged from the barrier drive ring, thereby allowing the barrier drive ring to rotate in the other direction to open the barrier blades by the spring force.
In an alternative lens barriers of the aforementioned type, the barrier drive ring is constantly biased toward one rotational end thereof to open barrier blades by a spring (first spring), while the barrier blades themselves are constantly biased in a direction to be closed by another spring or springs (second spring) whose spring force is smaller than the first spring. A rearward movement of the movable barrel of the zoom lens from the photographing position to the housed position causes another movable member of the zoom lens to be engaged with the barrier drive ring to rotate the same in one direction to restrict the spring force of the first spring, thereby allowing the barrier blades to be closed by the spring force of the second spring.
In these types of lens barriers, the barrier blades can be reliably opened and closed by a spring (biasing device) having a large spring force (large biasing force). However, the performance of the advancing/retreating operation of the movable barrel of the zoom lens, which moves between the housed position and the photographing position, deteriorates if the spring force is excessively large. This is because the driving force generated by a movement of the movable barrel between the housed position and the photographing position to drive the barrier blades is originally used to make the movable barrel itself advance to the photographing position or retreat to the housed position.
The difference between the photographing position and the housed position of the movable barrel can be regarded as the difference between two axial positions (two separate positions on the optical axis of the zoom lens) of the movable barrel, so that the barrier drive ring can be rotated by converting a linear movement of a movable member in the optical axis direction into a rotational movement about the optical axis. For instance, in a conventional lens barrier opening/closing device, a linearly movable barrel which moves in the direction of the optical axis without rotating about the optical axis is provided with an inclined surface which is inclined with respect to the direction of the optical axis, while the barrier drive ring is provided with another inclined surface which is inclined with respect to the direction of the optical axis. When the linearly movable barrel moves in the direction of the optical axis toward the barrier drive ring, the inclined surface of the linearly movable barrel is engaged with the inclined surface of the barrier drive ring which is pushed in the same direction, which causes the barrier drive ring to rotate about the optical axis. However, according to this structure, such an operation of converting a driving force in the direction of the optical axis into a rotational driving force about the optical axis results in a large energy loss. Accordingly, although the spring (biasing device) that biases the barrier blades preferably has a large spring force to reliably open and close as mentioned above, the performance of the advancing/retreating operation of the movable barrel of the zoom lens may deteriorate due to the large spring force since energy loss in an operation of transmitting a driving force from the linear movable member to the barrier drive is large. If the driving force for moving the movable barrel in the direction of the optical axis is increased to prevent this from occurring, an excessive load is exerted on a drive motor which drives the movable barrel.
There is further problem in such lens barrier opening/closing devices in which the barrier blades are opened and closed by rotation of the barrier drive ring. Namely, the lens barrier may not function properly if the rotational center of the barrier drive ring is eccentric from a predetermined position (generally the optical axis of the photographic optical system of the zoom lens). For instance, if the lens barrier is provided with a pair of barrier blades which are respectively pivoted at a pair of pivots fixed at different positions in a circumference of the lens barrier so that each barrier blade rotates about the corresponding pivot to be opened and closed, and if the barrier drive ring is provided thereon with a pair of engaging portions which can be respectively engaged with and disengaged from the pair of barrier blades, the pair of engaging portions of the barrier drive ring cannot be respectively engaged with and/or disengaged from the pair of barrier blades properly if the rotational center of the barrier drive ring is eccentric relative to the predetermined position. In this case, one of the pair of barrier blades may not be completely closed when the zoom lens retreats to the housed position, and/or may not be completely opened when the zoom lens advances to the photographing position.